The present invention relates to a new and distinct cultivar of Penstemon, given the name, ‘TNPENDB’. Penstemon is in the family Plantaginaceae (formerly Scrophulariaceae). This plant originated in a controlled breeding plan to create a compact series with good flowering. The parents are unknown, unnamed proprietary plants. This cultivar was selected for its dark purple foliage, short habit, lavender to violet flowers, hardiness, and vigor. It is an ideal plant for a sunny border in full sun.
Compared to plants of Penstemon digitalis, an unpatented plant, the new cultivar is shorter and more compact, flowers are more lavender to violet rather than white and foliage color that is tinted purple with winter temperatures rather than green.
Compared to plants of Penstemon ‘Mystica’, an unpatented seed strain, the new cultivar is shorter and more compact, flowers are more lavender to violet than white.
Compared to Penstemon ‘Dark Towers’, U.S. Plant Pat. No. 20,013, the new cultivar has a shorter and more compact habit, flowers are more lavender to violet rather than pink.
Compared to Penstemon ‘TNPENDV’, U.S. Plant patent application Ser. No. 15/932,827, the new cultivar has dark purple leaves instead of green leaves.
Penstemon ‘TNPENDB’ is uniquely distinguished by its:                1. glossy, dark purple leaves,        2. lavender to violet flowers,        3. short, compact, upright, well branched habit        4. attractive deep purple seed heads, and        5. excellent vigor.        
The new variety has been reproduced only by asexual propagation (cuttings and micropropagation). Each of the progeny exhibits identical characteristics to the original plant. Asexual propagation by cuttings and micropropagation using terminal and lateral shoots as done in Canby, Oreg., shows that the foregoing characteristics and distinctions come true to form and are established and transmitted through succeeding propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may vary with variations in environment without a change in the genotype of the plant.